Bear in mind...only a single Refresh point is gained at only Major Milestones.
Granted, in the game, that will happen with relative Frequency at least once every few years, if not once a year (or more if it's a particularly exciting and eventful). In most cases, the most powerful supernatural denizens of the Dresdenverse have existed for centuries, millennia, even eons. Most often with probably very little going on. When beings have eternity to plan and can wait just as long without consequence, their power gains will be LESS frequent, not moreso.
If anything, at power levels after say...20...there should only be a 1 refresh increase every OTHER power level.
20 Refresh will get you any of the watered-down versions of Senior Council members with room to spare. Or a stupidly powerful actual ninja ghoul. By that point, artificially inflating a character's power so steeply before play begins is just ludicrous. NO ONE spends their entire life in adventure. Even Han Solo spent most of his time on milk-run smuggling trips or high-stakes Sabacc games. Think of how much time goes between each novel...and how as the years drag on, sometimes those "dead spots" will span more years or even decades or centuries?
I would figure 15 might be better, since it'll almost get you those Senior Council members, but it's reasonable a group could cover 5 to 10 major milestones at least in a single story arc.
All that said...skills perhaps should continue at the same rate throughout... Refresh implies an increase in the fundamental POWER of oneself. Skills are just what you know...which you don't need high adventure to aquire...or normal people wouldn't even have average skills in anything at all.
Maybe after PL 30, skills start to taper off the same as refresh did at 15 or 20. After all, the more you learn, the less there is to be learned...from a practical study point-of-view anyway.
Frankly...I don't think any being directly encountered in the books would be higher than 50...tops. By that point, there's so little left to take that you're just going to have a big refresh gap to bank up fate points. Also, it would give most uber-powered monsters the free-will they're not supposed to have. While that might be cool for a deeply conflicted PC, it's not intended for NPCs. If you started a Wizard and got your hands on Seelie and Unseelie magic...they'd each only cost -2 (though, you wouldn't really "need" them, per se). After a certain point, most combinations of powers are redundant...especially when you get into spellcasting, as obviously many of the uber-baddies do in the novels. Yeah, I know more powers and stunts will be invented by groups because they're supposed to be...but still, something's gotta give. By 50 Refresh, you're toeing the line of munchkindom, and on a steady course for game-breakerville.
Now...realistically, you can take as many stunts and powers as you want...it's just that when you go to 0 or less Refresh, you get no more free will. So, I'd imagine that "monsters" start with 1 Refresh and never get more. They can acquire power out the wazoo...but they never gain new Refresh, and can only get Fate points from compels. Honestly, by the time people are pushing that 50 Refresh mark...any more power SHOULD make them lose their free will. That much power in a mortal or even semi-mortal vessel is just too much. You can't be a god with free will. Gods and the like are metaphysical maintenance robots, not people. And the uber-baddies are like diseases. Either way, once you get to a certain point, you pick a "side" and that's what your former character is forever stuck with...as you make your new character.
Dunno...just my take on it all. I just think it's kinda unreasonably greedy to INCREASE the refresh gained at higher PLs.
